Tagul and Wordle are great tools for creating word clouds.
Tagul is a little more versatile and has the benefit that each word can be a URL link.
The word clouds are created by entering either a text, URL or for Wordle a del.icio.us user name into a field. The site then generates a word cloud based on the frequency of key words in the text or web page.
These can be used for revision, discussion, vocabulary lists etc.
One example from Nik Peachey’s blog
Revision of texts – You can paste in short texts that your students have studied recently. Show them the word cloud and see if they can remember what the text was about and how the words were used within the text. You can build up a bank of word clouds over a semester and pull them out at random to get students to recall the texts they have studied and the key vocabulary in them. You could also see if they could rewrite or reconstruct the text based on the word cloud.
It is loads of fun and any text can be used to create a vibrant poster to start off a class on any subject.
Wordle: Pedagogical philosophy
The following one is from Tagul